The present invention is directed generally to an electronic grain moisture sensor for use in a grain-drying bin for measuring the percentage moisture content of grain at a position within the bin and for activating a discharge auger to remove a generally uniform layer of grain from the bottom of the bin when the measured percentage moisture content is lowered to a selected value.
The earliest electronic grain moisture testors were operated by direct current conductance. This method is accurate if moisture content is consistent throughout the kernel but rapid drying causes the outside of the kernel to be drier than the center thereby providing inaccurate results.
There are also several known ways to measure grain moisture content by oven drying. The fastest of these methods, however, requires three hours and a grinding of the grain which are unacceptable for an on-line control system.
The Karl Fischer titration method is a chemical test which is specific for water. This is probably the most accurate moisture measurement method but it would likewise not be practical for an on-line control system.
Microwave attenuation, while very accurate, is unsuitable because it is based on the dielectric loss factor which is not as consistent or well defined as the dielectric constant. Accordingly, expensive research would be required for development.
Most electronic equipment used for measurement of moisture in grain is based on capacitance measurement. The capacitance of a given sensor depends on the dielectric constant of the grain in the sensor. Since the dielectric constant for grain is much lower than the dielectric constant for water, a small amount of change in the amount of moisture in grain causes a relatively large change in its dielectric constant. This change in dielectric constant with grain moisture content makes it ideal for use in controlling drying equipment.
Most known grain moisture sensing devices require a sample of grain to be taken from the bin to an external testing unit or auger. This involves additional apparatus and expense and can introduce inaccuracies due to the limited quantity of the sample being tested. Finally, another problem with known grain dryer control systems is the need for frequent adjustment to accommodate for changes in ambient temperature and fan temperature and the inaccuracies which are introduced when such frequent adjustments are not attended to.
Accordingly, an object of the present invention is to provide an improved grain moisture sensor.
Another object is to provide such a sensor for accurately determining moisture content of grain for controlling the discharge of grain from a drying bin.
Another object is to provide an improved grain moisture sensor wherein moisture content is measured at a position within the bin adjacent the bottom wall therein so as to eliminate the need for removing a sample of grain to be tested externally of the bin.
Another object is to provide a grain moisture sensor of sufficient accuracy to minimize overdrying of grain.
Another object is to provide a grain moisture sensor which is simple and rugged in construction, inexpensive to manufacture, install and operate and which is efficient in operation.